Vascular disease, the disease of blood vessels, is one of the leading causes of death in the western world. There are two main categories of vascular disease, aneurysmal and occlusive. Aneurysmal disease results in the weakening of blood vessels causing them to dilate excessively and in some instances ultimately rupture. Occlusive disease results in blockage of blood vessels, limiting the conveyance of blood.
Stents and stent-grafts are commonly used to treat diseased blood vessels and other tubular structures within the body. Stents and stent-grafts have been employed successfully to either reinforce afflicted blood vessels in the case of aneurysmal disease, or to radially open and support blood vessels for the purpose of restoring blood flow in the case of occlusive disease. To such ends, stents and stent-grafts have been implanted in the coronary as well as peripheral vasculature. Additionally, stents have been implanted within the neurovasculature, and in other bodily conduits such as the urinary tract, the bile duct, and the tracheo-bronchial tree.
Current stent-grafts intended for the treatment of aneurysmal disease are generally available in various diameters. Several devices are available in bifurcated configurations. These bifurcated devices are typically designed for use within the aortic bifurcation, where the abdominal aorta branches into the right and left common iliac arteries. Frequently, this anatomic region is riddled by aneurysmal disease, causing a potentially life-threatening situation. In an effort to treat the potentially life-threatening situation, bifurcated stent-grafts are implanted within the aneurysmal regions of the afflicted vessels, essentially forming a new blood flow conduit within the aneurysm, and isolating the aneurysm from blood flow and the associated blood pressure. This is referred to as excluding the aneurysm. Similarly, aneurysms of the aortic arch and the thoracic aorta are also common.
Conventional stent-grafts, however, do not accommodate side-branches of the aorta. Once an aneurysm has been excluded, the entire diseased section of the afflicted vessel is isolated from normal blood flow. This isolation includes any side-branches emanating from the aorta within the afflicted region. While this may be a good outcome from the perspective of managing a potentially life-threatening situation, such isolation from blood flow can lead to ischemic complications in certain areas of the body. For example, emanating from the abdominal aorta distal to the renal arteries are lumbar arteries, testicular/ovarian arteries, and the inferior mesenteric artery, which provides blood to the left transverse colon, descending and sigmoid colons, and rectum. Many aneurysms of the abdominal aorta include the origin of the inferior mesenteric artery. After successful exclusion of these aneurysms, the left transverse colon, descending and sigmoid colons, and rectum rely on collateral circulation for their blood supply. For many patients, the collateral circulation is sufficient, but for others it is not, resulting in complications involving the various organs.
Additionally, many aorto-iliac aneurysms involve the abdominal aorta as well as substantial portions of either (or both) of the common iliac arteries. In many cases, the disease extends along the common iliac artery past the bifurcation point where the common iliac branches into the external and the internal iliac arteries. In such cases, the endoluminal treatment of the aneurysm may require extending the stent-graft device into the external iliac artery, isolating the internal iliac artery from normal blood supply and leaving large portions of the pelvic area and leg reliant on collateral circulation for their blood supply. For example, the hypogastric artery, which supplies blood to the pelvic area, branches from the internal iliac artery. Isolation of the hypogastric artery from normal blood flow can result in buttock claudication, impotence, and colon ischemia.
Aneurysms of the aortic arch, for example, can be especially difficult to treat using currently available stent-graft devices. Three major vessels originate from the aortic arch: the brachiocephalic, the left common carotid, and the subclavian artery. These vessels provide critical blood flow to the head, neck and arms. If a stent-graft device is endoluminally implanted to treat aortic arch aneurysms, adjunctive measures must be taken to ensure adequate blood supply to the body parts (especially the brain) that receive their blood supply from the affected vessels.
On the other hand, while in some instances isolation of a side-branch vessel via aneurysm exclusion results in compromised blood supply due to inadequate collateral circulation, in situations of abundant collateral circulation, the presence of a side-branch vessel can actually hinder aneurysm exclusion. Retrograde blood flow from side-branches emanating within the aneurysmal region can maintain blood pressure within the aneurysm, often resulting in leakage between the stent-graft device and the afflicted vessel.
Like stent-grafts intended for the treatment of aneurysmal disease, stent-grafts intended for the treatment of occlusive disease are generally tubular and available in various diameters. Such stent-graft devices offer the advantage of providing a physical barrier, which impedes reproliferation of the disease through the wall of the implanted device. The treatment of vessels aftlicted by occlusive disease at points of bifurcations, however, can be problematic due to the unpredictability of the vascular remodeling associated with balloon angioplasty and stent-graft implantation. In many instances, side-branches can be compromised as a result of plaque redistribution from the main vessel into the origin of the side-branch, resulting in stenosis of the side-branch.